For realizing a size reduction of a charge pump circuit, it is required to reduce sizes of circuit elements such as capacitors and switching elements, for example. The size reduction however lowers a voltage boosting ability. It is thus proposed to increase a frequency of an operation clock signal for attaining the size reduction while maintaining the voltage boosting ability.
An increase of the frequency of the clock signal results in generation of high frequency noises. For a vehicle application, in particular, it becomes difficult to meet a vehicle standard because of high frequency noises of an FM band, DAB band and the like.
For countering the high frequency noises, it is proposed to spread the frequency of the clock signal. For example, a frequency spreading circuit for spreading a frequency by adjusting a slope of a constant current is disclosed in the following patent document.
Patent document: JP 4240072 (US 2008/0032640 A1)
Since this conventional frequency spreading circuit is of a constant current type, it takes a certain period for stabilizing the current. Further, since a comparator is used, it is difficult to operate at high speeds, for example, over 1 MHz. Still further, since the conventional frequency spreading circuit needs a large number of circuit elements and is sized large, it is not suitable for application to small-sized products.